There are constant demands to increase the storage capacity of magnetic disk drives, which are used as storage units for computer systems and various kinds of electronic apparatus. In general, the magnetic disk drives are developed and designed with the goal of increasing the storage capacity.
In order to increase the storage capacity of a magnetic disk drive, it is necessary to increase the recording density of the magnetic disk. Known methods for increasing the recording density on a magnetic disk include increasing the density of the tracks along a radial direction of the magnetic disk (i.e., increasing the tracks per inch (TPI)), and/or increasing the density along the direction of the track (i.e., increasing the bits per inch (BPI)). Varying the track width of the magnetic disk at the inner periphery and the outer periphery of the magnetic disk, or depending on the width of the head, has also been proposed.
In addition to the demands for increased storage capacity, there are also demands for guarantee of large write/erase endurance. A “guaranteed write/erase endurance” refers to the guaranteed number of times data can be rewritten on the same position on a magnetic recording medium such as a magnetic disk.
When the track density on the magnetic disk is increased, the adjacent tracks become extremely close to each other, and if the recording head makes a recording or erasure with respect to one track, the adjacent tracks may also be affected. In a worst case, a significant portion or all of the adjacent track may get rewritten or erased. The adjacent track is affected by the recording or erasure because of the spread of the magnetic field of the recording head, and because the position of the recording head may become offset from the desired track position due to vibration and air flow.
For these reasons, it is difficult to guarantee a large write/erase endurance and also increase the track density. Consequently, a realization of a magnetic disk drive that is both inexpensive and has a large storage capacity has been difficult.